Variable potential electrical generator



J. H. COLEMAN VARIABLE POTENTIAL ELECTRICAL GENERATOR Filed OC'L. 30. 1948 Figi j E" im ATTORNEY Patented May 29, 1951 VARIABLE POTENTIAL ELECTRICAL GENERATOR John H. Coleman, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application october so, 1948,1seria1No. 57,463 Y 15 Claims. 1

This invention relates to electrical generators and more particularly variable potential nuclear electrical generators.

It is known that certain isotopes are radioactive and. emit nuclear charged particles at known rates over known periods of time and over a range of energy values or levels expressed in electron volts. Some emissions consist of positively charged or alpha particles, others of negativelyT charged or beta particles and others both alpha and beta particles."

When nuclear charged particles bombard or strike other substances, the particles cause secondary electron emission or other forms of sec.-

ondary radiation or the particle may be captured or elastically reected depending upon the energy and character of the particle, the angle of incidence of individua1 bombardments and the character of the bombarded substance itself.

\ Secondary electron emission `is in random directions and at velocities usually much less than that ofthe bombarding particles. `The paths of the secondary emission electrons depend upon their energies and the electrostatic and magnetic eld values in the region in which they move.

The change in potential of the radioactive source resulting from` its radiation depends upon the charge sign of the radiated` particles and intensity of the radiation. When a beta particle or electron is emitted from a source,`whether by primary or secondary emission thepotential'of the source with respect to the collector is posiing a magnetic field upon the medium betweenl the source and the electrode. This discharge is accomplished by the magnetic neld causing ionization of the medium, with attending flow of conduction currents of charged particles across the medium and thereby neutralizing the difference in potential between the source and the electrode. `These differences in potentials are utilized by connecting the source and the electrode to an external or load circuit.

Among the objects of the invention are to provide new vmethods of and means for generating variable electric potentials.

Another object of the invention is to build up at predetermined rates differences in potentials between a radioactive source and an electrode by the emission and capture of nuclear charged particles and to discharge the built-up potentials at predetermined values and at predetermined times andrates. v

' Other -objects will be apparent from the description of the invention as hereinafter'setforthj in detail andv from the drawings made Aa part hereofk in. .which Figurecl is a schematic sketch of a vertical cross section of an embodiment of the invention as applied to abeta emitter radioactive, source; Figure 2 is a schematic sketch of a vertical cross section of an embodiment of the invention as applied to an alpha emitter radioactive source.; Figure 3 is a graph showing the relation between the vvalues Vof the magnetic field impressed; upon the medium between the radioactive source and the collector electrode to the values of the potentials between the source and thewelectrode to satisfy the condition that the medium-is just non-conducting and a graph showingfthe relationvrbetweensthe difference in potential between the source and the electrode and time;V Figurefl Visa graph showingtherelation between` the strength of the magnetic field and time; Figure 5 isa graph showing the relationof theypotential.across-thedevceto time.; Figure 64 is a graphsliowingthe-relation` betweenthe curi-- rent across the device to the voltage across the device for a xed valueoimagnetic eld strength and a graph showing th'e'` relation of the voltage across the device to time; and Figure 7 is a graph showing the relation of\ the voltage across the 5device inrelationto time. z ,i

' Similar reference characters are appliedto similar elements throughout the drawings. .i

Referringto Figure 1, l represents the envelope. of the device', whichmaybe of glass or otherma'- terial permeable by .a magnetic` field and capable to maintaining a highjvacuum the rarified residual vgaseous medium having a kpressure notV exceeding lll-V3n mm. Hg, Yfor` example. The "imediumspecified throughout the specification and claims is intended to refer to said residualgascousv medium. Rod 2 is mounted in the verticalaxis of the envelope and has deposited thereon theradioactive material 3. Asfthis figure repre-` sentsthe embodiment of the device as applied to a betaV emitter, the radioactive materialmay be phosphorus, whichV is` 'apure beta. emitter with4 energiesV of fthefparticles` ranging up to. about 1 m. e. v. The radioactive material and the rod support 2 will be referred to throughout the specification and claims as the source and identied by the numeral 3.

Coaxial with source 3 is mounted the target or collector electrode 4 which is generally cylindrica1 in shape, with end plates 5` at each end extending inward. Collector 4 is made of some non-magnetic metal Which is also secondary electron emission responsive to beta radiation. Aluminum has .been found to be. satisfactory for this purpose. i

Surrounding envelope l is solenoid 6, which is connected to a source of direct. current 1. in the circuit of which is connecteda conventional! controlled interrupter Ill, such as a multi-vibrator.

Between source 3 and collectorl IlE is connected the load circuit of the device, a part of which circuit is a load having an impedance R. The.

load circuit and collector.. 5 are grounded at 8.

,In.operation, and-.referring.to.Eigures 1 and; 3, When there is no magnetic.- eld. impressedupon the medium of thefdevice, thebetal particles are emitted from source 3 in random directionsas illustratedby arrow 9, Because ofthegshape of electrodeli withY its end plates 5;. practically, all of. the particles'bombard or strike electrode 4. The, end plates 5,. are notabsolutely necessary toY the operation of this embodiment of the device, but. they increasethe, efciency, ofrelectron trapping. as Vwill be hereinafter explained.v

As each beta particle leavessource 3, a. unit positive chargeremains on source 3.and.as. each. beta particlev is. capturedy by electrode 4', the charge on thecollector. 4 is..decreasedcorrespond, ingly.A There will. be some secondary electron emission from collector 4.and theseelectrons Will be repelledby collector 4, thus tending to slightly decrease. thepotential. diierence` between. collector 4 and-source3. Some of, theseelectrons willbe accelerated toasource3, becausesource 3Y is of positive potential; However, therewill not be any ionization Othemediumof the device Las the mean free path ofthe electrons fori/collision with4 the. molecules.. off the medium is-..much less*- than the meanpath between molecules of the va=2r 1) where .Va,. is. the .voltageiacross.the;.device, i..is .the radioactive current, c is.the. capacityV ofi the systemand T is time. The sma1l.-,currents,.due..to secondary emission.v arev subtracted. from.. the radioactive. current to determiner the.. eiective generated currents. The plot. ofi this .relation is shown in thelower# half.A of ligureB.A

When aV magnetic eld is impressedL uponA the medium of the device,A as indicatedby the arrow H; for certain values O'Hand-Va the secondary electrons areY cut oir fronr reaching `source 3iby being so deected intheir paths, that they pass by source 3 and` strike electrode. 4" again and again.A They are therebyA trapped'. withinv the medium and their paths'arehlengthenedlbeyond theme11 free, path ionization byk collsionand ionization .0f themesiium .Occurs With 1011i@- t99 futhfzr, orlcumlllapie' ionization-.9061.155 be causeI ofv the' creation of a large number orion mi cl'e, e is the charge of the particle and Va is the 4, pairs and large conductive currents flow across the medium.

The conditions for cut olf have been calculated to be Rs ST1 where Rs is the radius of source 3, Rc is the radius of electrode 4, m is the mass of the partipotential ofsource 3, al1 in c. g. s. units (see Hull, Physics Review 1921, Volume 18, page 35).

In the upper; part of Figure 3, there has been plotted by the dash curve the observed conditions, of a. particular tube, of cut off for various values of II and Va.. The lower part of this curveV corresponds closely to the mathematical analysis of the reactions as set forth in Equation 2.

Thus, if after an intervalof time, tu Va will have risen;` to the value of Vr and; ifr a magnetic eld' is impressed upon thev` medium at the timeY instant of t1 and equal. to or greater; than Ho (see Figul'e 4'), the medium becomes conductive (seeFigure 3) and Vawill dropthrough the conf. duction region to near Zero in the time interval' nt,Y This discharge period is determined' by At=RfG (3)Y where R is the eiective resistance, of the cori-- duction` region and C, is the total. efectivecapacity of the system.

If.; the solenoid, circuit is, brokenv at the end of.

the periodALl-I becomeszero. and the devicewill .begin` to recharge again at aV constant rate as.

hereinbefore described.

In Figure is showna typicalmagnetic.pulse, which is afunction of, thecur-rent throughthe. solenoid. It is obvious. that thisl pulse may be biasedA by a.` magnetic ieldA equal to.v any value below that of- Ho.

The plot oflthe Valversus. time is shown inFig. ure.5l-

The. devicev shown in Eigure. 2; is; useds whenv thel radioactive material v is an-V alpha,A emitter. Thev arrangements of the twol devices are` gen-,-

erally the..same.excep,tthat. the plates forming.

the-.ends of. the conductiveregion for thealpha emitter are essential. and-are made.v part of the.

central electrode instead of. the outer electrode, as. inA the.v case; oi a, beta emitter. thatl no. trapping.L or; ionization occur-redA Within the=.medium, with attending conduction* currents; if the locations i of.n the endplates-were; reversed,

thatis, if the plates were secured to theelectrode.

4.in. an alpha emitter. device., andvicev versa,V

rod. or. .electrode -upronl which is vdeliosited theradioactivematerial; PoloniumZlU-is a suitable alphaemitter.v with radiated particles;reachingmaxi,- mum-enerey Valuespiebouta mf. e. v.

At` each.. end? ot electroder 2L are positioned the; eed, plates-15.. 4-isithe Collector electrode-andis'y cylindrical; in v shape. 'Il he. solenoid i ysupplied by-v direct. currentfrom source l, surroundsfthe enve-.-

emission-which, are immediately returnedt to. the.

collector by the electriceld., The deltaelectrons emitted from.. the. Seurce. tend to. .be Y attractedtto the positive collector 4.

Itwasgfound- The generation of large conduction currents upon the .impressing of a magnetic eld upon the medium occurs in the same manner as hereinbefore described, except that the delta electrons and ionization electrons flow to the electrode 4 and therefore ovv through the medium and the load circuit in a direction opposite to that when a beta emitter is used as the radioactive source.

The solid curve in Figure 3 is a plot of theI relationbetween the magnetic field H and the voltage across the device, when the device is just non-conducting. The value of the magnetic, field to cause the generation of conduction currents when Va reaches the value of VI, is determined from the graph as Hl. The sawtootnvoltagetime curve in Figure 5 applies to both types of devices.

. To dene the relation between a time interval of charging the device and the minimum required magnetic eld for discharge of the device at the end of that time interval, it will be noted from the form of the lower boundary of the alpha (solid line, Figure 3) cut-off curve that H =KVVa (3') where K is a constant determined by the geometry of the elements of the device.

It has been seen that and as i and c are constants determined by the amount ci radioactive material deposited on electrode 2 (disregarding the half -life of the radioactive material) and the capacity of the system, respectively, Equation 1 becomes and for the alpha case Where Kz=K\/K'.

For the beta device, where V .Vo, H=Ho=a constant.

As another method of operation (see Figures 6 and 7), the magnetic eld is held constant at some value, for example, H2, Figure 3. Referring to Figure 6 there is plotted again in the lower part of the figure, the charging curve (a straight line) of Va versus time.

When the charging voltage Va reaches the value Vo at time (tu) a small amount of current (in) will begin to flow across the device. As Va increases the effective resistance across the device becomes less and less and the current increases rapidly, as plotted in the upper part of Figure 6. With the larger currents flowing the voltage across the device, Va, drops almost to zero, asV shown in Figure 7, in which is plotted the relation between Va and time (T) It is of course apparent that a wide range of desired outputs both as to voltage values and the form of the voltage-time curves can be obtained byselecting different amounts of radioactive material and selecting the geometry oi the elements of the device.

Likewise, in selecting a biasing magnetic field, its value may approach the lower cut off value and, in such cases, the secondary electrons emitted from the collector electrode (beta emitter case) returned by the magnetic eld to the collector and the delta electrons (alpha. emitter case) are returned to the source. In both cases, the charging rateis increased, Y

There is thus disclosed an invention for providing variable potentials of desired values and Wave forms by utilizing the potential charges on particles emitted from a radioactive isotope and controlling the flow of accumulated charges by a magnetic field.

What is claimed is:

1. The method of creating variable electric potentials comprising: providing a source of nuclear charged particle radiation in a raried gaseous medium, exposing-to said radiation a secondary electron emissive material, whereby diierences of potentials are created between said source and said material by the emission of the said particles from the source and the capture of said particles by the saidmaterial, and imposing a magnetic eld upon said medium at intervals of time, whereby the medium becomes conductive and the said created potentials are neutralized. Y

2. The method of creating variable electric potentials comprising: providing a quantity of a radioactive isotope in a rarled gaseous medium, exposing to the charged particle radiation of said isotope a secondary electron emissive material, whereby diierences in potentials are created between said isotope and said material by the emission of the said particles from said isotope and the Vcapture of said particles by the said material, and imposing a magnetic eld upon said medium at intervals of time, whereby the medium becomes conductive and the said created potentials are neutralized.

3. The method of creating variable electric potentials comprising: providing a quantity of radioactive isotope in a rarified gaseous medium, the quantity of said isotope being in proportion to the desired rate of increase in potentials of said variable potentials, exposing to the charged particle radiation of said isotope a secondary electron emissive material, whereby diierences in potentials are created between said isotope and said material by the emission of the said particles from said isotope and the capture of said particles by the said material, and imposing a magnetic eld upon said medium at intervals of time, whereby the medium becomes conductive and the said created potentials are neutralized.

4. The method of creating variable electric po'- tentials comprising: providing a quantity of a radioactive isotope in a raried gaseous medium, exposing to the charged particle radiation of said isotope a secondary electron emissive material, whereby differences in potentials are created between said isotope and said material by the emission of the said particles from said isotope and the capture of said particles by the said material, imposing a magnetic eld upon said medium at intervals of time, whereby the medium becomes conductive and the said created potentials are neutralized by the ilow of conduction currents between said isotope and said material, and adjusting the electrical characteristics of the circuit in which the said conduction currents flow to control the rate of said llow and thereby Y the rate of neutralization of said created potentials.

5. The method of creating variable electric potentials comprising: providing a quantity of a radioactive isotope in a raried gaseous medium, the quantity of saidV isotope being in proportion to the desired rate of increase in potentials of said variable potentials, exposing to the charged particle radiation of said isotope a secondary electrongemissive material, whereby diierences in 'assaut 177` potentials are created between said isotope and said material by the emission of the said particles from said isotope and the capture of said particles by the said material, imposing av magnetic eld upon said medium at intervals of time, whereby the medium becomes conductive and the said created potentials are neutralized by the flow of conduction currents between said isotope and said material, and adjustingv the electrical characteristics of the circuit in which the said conduction' currents now tosaidv controll the rate of:v said flow and thereby the rate of neutralization of said created potentials.

6. The method oi ,creating variable electric potentials comprising: providing a source of nuclear charged particle radiation in a rariiied gaseous medium, exposing to said. radiation a, secondary electron emissive material, whereby differences of potentials. are created between said source and said material by the emission of the said particles from thesaid source and the capture of said particles by the said material, and` imposing a constant magnetic neld upon said medium, wherebythe medium becomes conductive upon the said potentials rising to. predetermined values and the said created potentials are neutralized.

7. The method of creating variable electric potentials comprising: providing a quantity of radioactive isotope in a raried gaseous medium, exposing to the `charged particle radiation of-said isotope a. secondary electron emissive material, whereby differences in potentials are created between saidl isotope and said material by the emission of the said particles fromsaid isotope and the capture of said particles by the said material, and imposing a constant magnetic field upon said` medium, whereby th-e medium becomes conductiveupon the said potentials rising to prede.- termined values and the said created potentials are neutralized.

8. The method of creating Variable electric potentials comprising: providing a quantity of radioactive isotope in a raried gaseous medium, the quantity of said isotope being in proportion to the desired rate of increase in potentials of said variable potentials, exposing to the charged particle radiation of said isotope a secondary electron emissive material, whereby differences in potentials are created between said isotope and said material by the emission of the said particles from said isotope and the capture of said particles by the said `material, and imposing an ionizing constant magnetic eld upon said medium, whereby the medium becomes conductive upon the said potentials rising to predetermined values and the lsaid created potentials are neutralized.

9; The method of creating variable electric potentials comprising: providing a quantity of radioactive isotope in a raried gaseous medium, the quantity of said isotope being in proportion to the desired rate of increase in potentials of said variable potentials, exposing to the charged particle radiation of said isotope a secondary electron emissive material, whereby differences in potentials are created between said isotope and said material by the emission of the saidr particles from said isotope and the capture of said particle by the said material', imposing a constant magnetic field' upon said medium, wherebyflthe medium becomes conductive upon the said potentials rising to predetermined values and the said created potentials are. neutralized lbyV the flow .of conduction cur rents .between saidisotope and said'material,4 and adjusting the electrical characteristics. of the circuit in which the said conduction currents now to control the rate offsaid flow and thereby the rate of neutralization of said created potentials;

10. Apparatus for creating variable electrical potentials comprising: a magnetic field permeable envelope enclosing a rarified gaseous medium, a source of nuclear charged particle radiation in said envelope, a secondary electron responsive electrodepositioned adjacent said source, a solenoid surrounding said envelope and connected to a source of direct current suicient to provide a magnetic field to ionize said medium, means to supplysaid current at predetermined intervals to said solenoid, and a load circuit connected between said source and said electrode 11. Apparatus for creating variable electrical potentials comprising a magnetic eld permeable envelope enclosing a rariiiedA gaseous medium, a source of nuclear negatively charged particle radiationk being cylindrical in shape and positioned along the axis of said envelope, a secondary electron responsive electrode positioned adjacent said source, a solenoid surrounding said envelope and connected to a source of direct current Asunicient to provide a magnetic iield t0 ionize said medium, means to supply said current at predetermined intervalsy tov said solenoid; and a load circuit connected between said source and said electrode. vf 12. Apparatus for creating variable electrical potentials comprising: a magnetic eld permeable envelope enclosing a raried gaseous medium, a source of nuclear positively charged particle radiation being cylindrical in shape and posi.- tioned along the axis of said envelope, a secondary electron responsive electrode positioned adjacent said source, a solenoid surrounding said envelope and connected to a source of direct current suiiicient -to provide a magnetic field to ionize said medium, means to supply said current at' predetermined intervals to said solenoid, and a load circuit connected between: said source and said electrode.

13. Apparatus for creating variable electrical potentials comprising: av magnetic iield permeable envelope enclosing a raried' gaseous medium, a source of nuclear negatively charged particle radiation positioned along the axis of said envelope, a secondary electronv responsive electrode positioned adjacent said source, the said electrode beingV cylindrical in shape and coaxial with *saidv source and having end plates extending toward said source, a solenoid surrounding said envelope and connected to a source of direct cur-,- rent suicient to provide a magnetic field to ionize said medium, means to supply said current at predetermined intervals to said solenoid, and a load circuit connected lbetween said source and said electrode. Y

1 4. Apparatus for creating variable electrical potentials comprising: a magnetic eld permeable enclosing a rariiied gaseous medium, a source of nuclear positively charged particle radiation, the said source being cylindrical in shape and positioned along the axis of said envelope, thesaidsource having at eachend lateral flanges that extend .outward from the source toward said envelope, al secondary electron responsive electrode positioned adjacent said source, a solenoid ysurrounding said envelope and connected to a source of direct current sufficient to provide a magnetic field to ionize said medium, means to supply said current at vpredetermined intervals -to said solenoid, and a. load circuit connected between said source and said electrode.

15. Apparatus for creating variable electric potentials comprising an envelope containing a raried gaseous medium, a source of nuclear charged particleradiation enclosed therein, a secondaryelectron-emissive electrode within said envelope exposed to said radiation, 'whereby in operation differences of potentials are created between said source and said electrode by the emission of said particles from Said source and capture of said particles by said electrode, and means for applying a magnetic eld to said medium at intervals of time, whereby the medium becomes conductive and the said created potentials are neutralized.

JOHN H. COLEMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,108,830 Skellett Feb. 22, 1938 2,128,408 Grenier Aug. 30, 1938 2,492,313 Okress Dec. 27, 1949 OTHER REFERENCES The Electrician, Oct. 31, 1924, page 497. 

